That the Chaffinch is one of our most familiar birds reflects its sizeable population – some six million territories – and the broad range of habitats within which it breeds. It is also a regular garden visitor, attracted to seed provided in hanging feeders and on bird tables, with gardens also used for nesting.
What’s in a name?
The Chaffinch’s scientific name Fringilla coelebs was assigned by Linnaeus in 1758 and makes reference to the bird’s migratory behaviour; ‘coelebs’ means ‘unmarried’ and Linnaeus gave the Chaffinch this name when he observed that the individuals wintering around his home in Sweden were male birds. The females from northern breeding grounds wintered further south than the males, a pattern of behaviour known as differential migration – where one sex or age class shows different migratory behaviour to another. Generally, we see females and juveniles winter further south than males and adult birds, suggesting that competition for resources may limit which classes can winter at higher latitudes.
Warts and all
It is not unusual to see Chaffinches with leg growths, some of which can make one foot and/or leg appear much larger than the other. The growths are often grey or off-white in appearance and rather ‘crusty’ in outline. There are two main causes of these growths in British and Irish Chaffinches: some are caused by mites belonging to the genus Cnemidocoptes, while others are the result of a virus called Chaffinch papillomavirus. The symptoms are fairly similar in their appearance and there is evidence to suggest that both conditions can occur together in some individuals. Although most individuals showing signs of these diseases are bright, active and able to feed, some birds become lame and others may suffer from secondary bacterial infections. While captive birds with mites can be treated it is not possible to target wild birds with an appropriate dose of the medicines used to treat the disease, which leaves good hygiene practice at garden feeding stations as the recommended means to reduce the impact of these diseases. More advice on this is available from the Garden Wildlife Health project website (PDF), a partnership project with which the BTO is involved.
A downturn in fortunes
The recent declines seen in Chaffinch populations, as revealed through the BTO/JNCC/RSPB Breeding Bird Survey (BBS) and BTO Garden BirdWatch, show a change in fortunes for a species whose populations had increased over recent decades. We know that Chaffinch populations were hit by the 2006 outbreak of finch trichomonosis (see the BTO research papers on this disease outbreak), with a decline of 21% recorded in the regions with the highest levels of disease incidence. Things seemed to improve after a couple of years, with the BBS index back up to pre-outbreak levels but there was a noticeable decline in the index in 2013 and 2014, a pattern also reflected in the weekly BTO Garden BirdWatch results for the same period. Could this have been linked to finch trichomonosis?
It is well known that the plumage of the male Chaffinch changes through the course of the year, the birds being at their finest ahead of the breeding season. Interestingly, the steely-blue colouring of the head and nape, which contribute to the breeding plumage, is not produced by the bird moulting through new feathers. Instead, the colouring appears as the dull brown-coloured feather tips wear away to reveal the colour that had been hidden below. Individuals of the British and Irish race are slightly smaller but more brightly coloured than the continental immigrants who arrive to join our resident birds in late autumn. These arrivals often bring smaller numbers of the related Brambling with them, a real treat for garden birdwatchers. Arrivals of both species may be influenced by the size of the beech mast (seed) crop across Europe. In those years when the crop is poor we see more individuals arrive here, with many moving into gardens to take sunflower hearts and high energy seed mixes.